In recent years, a dipeptidyl peptidase IV (DPP-IV, hereinafter) inhibitor has been drawing attention as a therapeutic agent for diabetes mellitus (particularly type II diabetes mellitus), and a large number of derivatives having DPP-IV inhibitory action have been reported. Particularly, since aminoacetylpyrrolidinecarbonitrile derivatives show an excellent blood sugar lowering action, several compounds promising as antidiabetic agents have been reported. It is general that these aminoacetylpyrrolidinecarbonitrile derivatives are produced by allowing 1-(2-chloroacetyl)pyrrolidine-2-carbonitrile or 1-(2-bromoacetyl)pyrrolidine-2-carbonitrile to react with a corresponding amine in the presence of a base (Patent References 1 to 16).
On the other hand, as a production method which does not use 1-(2-chloroacetyl)pyrrolidine-2-carbonitrile or 1-(2-bromoacetyl)pyrrolidine-2-carbonitrile, a method has been disclosed in which an aminoacetylpyrrolidinecarboxamide derivative is produced and then an aminoacetylpyrrolidinecarbonitrile derivative is produced by carrying out a dehydration reaction (Patent References 10 to 13, Patent References 17 to 19). However, the Patent References 10 to 13 do not illustratively describe with regard to the synthesis method of an aminoacetylpyrrolidinecarbonitrile derivative through a dehydration reaction of an aminoacetylpyrrolidinecarboxamide derivative, and the Patent References 17 to 19 describe only an illustrative example of carrying out the dehydrating reaction using an intermediate in which a protecting group is introduced into an amino group.    Patent Reference 1: JP-T-2000-511559 (the term “JP-T” as used herein means a published Japanese translation of a PCT patent application)    Patent Reference 2: JP-T-2002-531547    Patent Reference 3: JP-A-2002-356471 (the term “JP-A” as used herein means an unexamined published Japanese patent application)    Patent Reference 4: JP-T-2004-500321    Patent Reference 5: JP-T-2005-529078    Patent Reference 6: JP-T-2004-503531    Patent Reference 7: US 2002/019339    Patent Reference 8: WO 04/099185 pamphlet    Patent Reference 9: WO 05/075421 pamphlet    Patent Reference 10: WO 02/38541 pamphlet    Patent Reference 11: WO 03/095425 pamphlet    Patent Reference 12: JP-A-2004-26820    Patent Reference 13: JP-A-2006-160733    Patent Reference 14: JP-A-2002-356472    Patent Reference 15: JP-A-2004-2367    Patent Reference 16: JP-A-2004-2368    Patent Reference 17: WO 03/057666 pamphlet    Patent Reference 18: WO 04/026822 pamphlet    Patent Reference 19: WO 06/043595 pamphlet